Launchpad, can't set decks C & D to UNLOAD

I am trying to have 2 buttons for decks C & D to unload tracks in Traktor on my launchpad. I want the play buttons to be the unload buttons with the use of the modifier button I have set up. It seems to work fine for decks A & B (which I doubt I'll ever need to unload), but decks C & D (which I might need to unload from time to time) won't have it.

I have the play buttons set up with the modifier 1 button set to zero, and the unload option set to the same buttons as play, only with the modifier 1 option set to 1. This is how I did it for decks A & B and it worked first time. Any ideas why decks D & C won't have it?

Thanks